Hierarchical Ni@Ni(OH)2 core-shell hybrid arrays on cotton cloth fabricated by a top-down approach for high-performance flexible asymmetric supercapacitors

Abstract

A simple and cost-efficient top-down strategy is used to prepare a high conductive Ni microspheres @ Ni(OH)2 nanoflakes core-shell on cotton (Ni@N NF-CT) flexible electrode via a palladium-free catalytic electroless deposition process followed by electrochemical oxidation with further optimized cyclic voltammetry cycle times. Taking the advantages of the interfacial Ni microspheres and Ni(OH)2 nanoflakes which accelerates the electronic transport through the increased electro-active surface and the shortened ion diffusion distance, the as-prepared electrode exhibits the outstanding electrochemical performances such as ultrahigh areal specific capacitance (5.17 F cm−2/0.53 mAh cm−2 at a current density of 5 mA cm−2), the high rate capability (78% capacitance retention at a current density of 25 mA cm−2) and the well cycling stability (89.5% capacitance retention after 1500 charge/discharge cycles). A flexible asymmetric supercapacitor (FASC) is successfully fabricated using Ni @ Ni(OH)2 core-shell on cotton as the positive electrode and active carbon cloth (ACC) as the negative electrode, which manifests a high energy density of 0.597 mWh cm−2 (1.91 F cm−2/1.44 mAh cm−2) at a power density of 3.68 mW cm−2 (5 mA cm−2) in 2.0 M KOH aqueous electrolyte. The device is also super flexible as demonstrated by powering the red LEDs under various bending conditions. This facile fabrication process demonstrates the low-cost production of Ni @ Ni(OH)2 core-shell on cotton as a promising material for application in the high-performance flexible electrochemical energy storage devices.